This application claims priority to International Application No. PCT/GB00/03051 filed Aug. 8, 2000. The International Application was published in the English language on Feb. 22, 2001 as International Publication No. WO 01/13497 and itself claims the benefit of United Kingdom Application No. 9919018.3 filed Aug. 13, 1999.
This invention relates to an assembly of first and second rotatable members and more particularly but not exclusively to such an assembly which may be utilised for cooling e.g. an internal combustion engine.
Conventionally such engines are cooled with a coolant such as water, which is pumped through a water jacket and/or cooling fluid passages of the engine. The cooling fluid is cooled by being passed through a radiator, through which air may pass. The air may pass through the radiator due to movement of a vehicle driven by the engine, but usually a fan is provided to force air through the radiator, even when a vehicle is stationary.
It is known for the fan to be driven directly from the engine via a transmission such as a fan belt, but in modern high performance engines, more commonly, such cooling fans are electrically driven by an electric motor. The fan speed is usually constant when running, but the fan is switchable on and off under the control of a simple thermostat which senses cooling fluid temperature. Thus the fan is not switched on until required. However using a simple thermostat controlled fan, it is not possible to control the temperature of the engine with any accuracy, particular it is not possible to control the fan so that the engine temperature remains within a predetermined temperature range.
It is also known to drive an impeller of a coolant pump directly from the engine, but again in modern high performance vehicles, it is more usual for the coolant pump to be electrically driven. Usually the coolant pump is arranged to operate whenever the engine is operating, although may be controlled e.g. by a thermostat control or the like, if desired.
Thus typically the coolant pump and cooling fan are physically separate and are controlled separately via distinct controllers.
According to a first aspect of the invention we provide an assembly including first and second rotatable members which rotate about a common axis of rotation, the first member being connected to a first rotor and the second member being connected to a second rotor, the first and second rotors being concentrically arranged, the assembly further including a first stator including coils wound about a core, and a second stator including coils also wound about the core, the first rotor being rotatable in response to electrical current flowing in the coils of the first stator and the second rotor being rotatable about the axis in response to electrical current flowing in the coils of the second stator.
Thus utilising an assembly of the invention, particularly but not exclusively where the first rotatable member is an impeller of a coolant pump and the second rotatable member is a cooling fan, engine cooling for example may be achieved more efficiently as the assembly can be made more compact than in an arrangement having a physically separate coolant pump and cooling fan, and by virtue of the coils of the first and second stators being wound on a common core, the assembly is considerably economically advantageous.
Preferably the stator core is constructed so that the coils of the first stator are separated from the coils of the second stator so as to provide no or minimal magnetic interference. The core may also be optimally designed to provide separate magnetic circuits for the first and second stators.
Although many different stator winding configurations are possible, the stator core may include first radially extending formations about which coils of the first stator are wound, and second radially extending formations about which coils of the second stator are wound. The formations may be so called xe2x80x9cteethxe2x80x9d which are affixed at one end to a generally circular stator core part, and are free at their opposite ends to have the coils wound thereon. The first radially extending formations may extend radially inwards from the circular stator core part, and the second radially extending formations may extend radially outwardly from the circular stator core part.
Thus the second radially extending formations may be positioned radially outwardly of the first radially extending formations.
Although many different core constructions are possible, preferably the core includes at least two core parts which are assembled upon relative axial movement, e.g. by axially extending fasteners connecting the two core parts together.
The stator core may be generally cylindrical having a generally central opening in which at least part of the first rotor is rotatably received, and the second rotor may include a rotor housing part which rotates externally of the stator core.
The second rotor may include a radially extending wall, and generally centrally of the radially extending wall the second rotor may have an axially extending part by which the second rotor is rotatable about the axis of rotation.
Thus the first rotor may include an axially extending hollow in which the axially extending part of the second rotor housing is received for rotation.
In this way the axial extent of the assembly may be minimised thus enabling a very compact design to be achieved.
Again various geometries are possible although preferably the first rotatable member is connected to the first rotor so as to rotate at a first axial end of the assembly and the second rotating member is connected to the second rotor so as to rotate at or towards a second axial end of the assembly. Thus the radially extending wall of the second rotor housing may be positioned in the second axial end of the assembly.
It will be appreciated that the first storage and first rotor are in effect two components of a motor, and the second stator and second rotor are two components of a second motor the stators sharing a common stator core. Both motors of the assembly are preferably brushless and the first rotor is rotated solely as a result of the flow of electrical current in the coils of the first stator and the second rotor is rotated solely as a result of the flow of electrical current in the coils of the second stator.
If desired a control means may be provided which is operative to control the supply of electrical current to the coils of the first and second stators.
Thus whereas with an arrangement which utilised a separate pump and cooling fan for example, separate controllers have been used but with the provision of the assembly of the invention, a single control means may be provided thereby simplifying construction.
In one embodiment the control means is adapted to supply electrical current in a predetermined sequence to sets of coils of the first stator whereby the first stator and first rotor of the assembly are a first switched reluctance motor. The control means may be adapted to supply electrical current in a predetermined sequence to sets of coils of the second stator too whereby the second stator and second rotor of the assembly are a second switched reluctance motor, and the control means may be adapted to control the supply of electrical current to the coils of the first and second stator independently.
The invention may be applied wherever it is required to provide two rotatable members in a compact assembly. However, the invention particularly lends itself to an arrangement in which the first rotatable member is an impeller of a fluid pump and the second rotatable member is a cooling fan, the cooling fan being operated to cool the fluid pumped by the pump. More especially the assembly may be adapted to be mounted so that the cooling fan directs cooling air through a radiator of a cooling system to cool cooling fluid pumped through the radiator by the pump.
To reduce the requirement for dynamic seals and the like to prevent pumped coolant leaking along the first rotor into the stator core, preferably the fluid which is pumped by the impeller is permitted to pass into a generally annular space exterior to the first rotor. Thus seals are only required to prevent the fluid leaking into the stator coils, but such seals may be static seals which are more easily and economically provided.
According to a second aspect of the invention we provide a system including an assembly according to the first aspect of the invention, the system further including a plurality of sensor means which provide inputs to the control means which responds by controlling the operation of the first and second rotatable members.
Thus utilising an assembly of the first aspect of the invention, a system which may be intelligently operated may be provided. For example, the control means may be adapted to control the speeds of rotation of each of the first and second rotatable members in dependence upon the inputs provided to the control means to optimise the performance of the system.
The system may be a cooling system, the assembly including an impeller to pump coolant, and a cooling fan in which case the speed of rotation of the impeller which pumps the fluid and the speed of rotation of the cooling fan may be controlled to maintain the temperature of the fluid in the system either below a maximum temperature or within a predetermined temperature range.